A substantial number of commonly used and well known industrial processes involve transporting various media in pipes, and storage or separation of these in tanks or vessels, in particular pressurized tanks or vessels holding media under high pressure and at elevated temperatures. Determination of the type and character of the media contained in the tank or vessel by electronic means is a substantial element for managing and controlling such processes.
In several applications it is of importance that measurements can be made through a wall of a pressurized container. This applies to various industries, such as e.g. to the petroleum industry or the food industry. In the petroleum industry, it will be advantageous to be able to determine the relative composition of water, hydro carbons in various states, and gas using a probe positioned in the interior of a vessel or installed in a pipe wall. Similarly, a plurality of sensor devices according to the invention could advantageously be located at different levels in a tank, pipe, or vessel, to determine the composition of the media contained therein at corresponding levels, such as e.g. in a separator tank for processing and separating the various phases in a multi-phase flow from a hydrocarbon well. Thereby, that the level of water, gas, and oil within the tank may be determined on a continuous basis, and without interrupting a process involving the media. Typically, there will be considerable dynamics in a separator container when processing a production stream, such that distinct levels or clear interfaces between the various phases of the media contained in may not be formed. By applying electrical measurements based on a variation of electrical capacitance of an electrical capacitor of which the media in the pressurized container forms at least a part of a dielectric between the plates of the capacitor, the condition that the respective dielectric constant, herein also referred to as the electrical permittivity, of water, oil, and gas phases are widely different from each other is exploited, such that the relative portions of the different phases in a mixture at levels of interest within the container may be inferred.
In known solutions where relative portions of the different phases in a mixture at levels of interest within the container are inferred from electrical measurements based on a variation of electrical capacitance value C of an electrical capacitor as a function of the effective dielectric constant of the media to which the capacitor is exposed, the electrical capacitor of electrical capacitance value C is coupled with an inductive element of electrical inductance value L to form an electrical resonator having a resonance at angular frequency w that generally is generally given by w=(C*L)−1/2. The angular frequency w at resonance, which is measured to infer the relative portions of the different phases in the media composition, hence, varies not only proportionally with the square root of the electrical capacitance value C of the electrical capacitor, but also proportionally with the square root of the electrical inductance value L of the inductor. Accordingly, the stability and accuracy of the frequency w to be measured as a function of the capacitance value C of the capacitor that is exposed to the media in the tank or container, greatly depends on the degree to which the inductance value L of the inductor may be controlled and kept stable for a measurement period, and sensitivity of the inductor to stimuli due to mechanical vibration and other environmental conditions that have an effect on the inductance value L of the inductor. In the case of monitoring the processing of a hydrocarbon well stream, or other fluid that is streaming or being pumped to a tank or container, typically at high or rapidly varying velocities, rapidly varying and powerful mechanical impulse and vibration noise is generated and inevitably coupled to the resonator circuit of the sensor, and requires complex or intricate mechanical, electrical and signal processing designs in order for the noise to filtered out or compensated for in the signal for measuring the frequency of the resonator.
Accordingly, there is a need for an improved apparatus and method for measuring a parameter related to electrical permittivity of a fluid or fluid media composition in a container.
The invention is in part enabled by the recent development of semiconductor based miniaturized circuitry, allowing for the provision of an ultra-accurate power supply using commercially available electronic components.